The present invention relates to an insulating material for forming a main insulation for windings of electrical machines, windings for electrical rotating machines using the insulating material, and a method for manufacturing the windings.
JP-A-63-110929 (1988) discloses a method of forming insulating film for electrical windings used in electrical rotating machines by applying an insulating material to a conductor bundle, which comprises a mica layer, a reinforcement layer, a filler layer containing fillers having a high thermal conductivity therein, and each of the layers contains thermosetting resin.
The insulating material is wound around the wound conductor bundle, and the insulating film for windings of electrical machines is formed by curing the resin in the insulating material under heating and pressurizing. The windings for electrical machines is manufactured by the steps comprising wrapping the conductor with the insulating material which comprises the above mica layer, reinforcement layer, and filler layer; impregnating thermosetting resin composition containing fine divided inorganic filler into the insulating layer; and curing the resin composition by heating under pressurizing.
Furthermore, a method is disclosed, wherein a thermosetting resin composition containing fillers is impregnated into or applied onto the mica foil before wrapping the conductor with the mica layer containing the reinforcement layer.
JP-A-55-53802 (1980) discloses an insulating material, wherein a synthetic fiber fibrid and a high heat conductive inorganic powder are mixed into bonded mica sheet, and a thermosetting resin is impregnated therein. The publication discloses an insulating sheet, which is formed by adhering glass cloth to the mica paper with epoxy resin.
The winding of electrical machines formed as described above using the insulating material does not have any problem as far as it is used for the electrical rotating machines operated at a low voltage. However, when the winding is used for electrical rotating machines operated at a high voltage such as commercial power generators, high voltage motors, and the like, electrical defects of the winding sometimes cause problems. The inventors of the present invention have investigated reasons why the electrical defects of the insulating material were caused.
As a result, it was found that when the insulating film for windings of electrical machines is formed onto the conductors, followed by curing under heating and pressurizing, a part of fine bubbles contained in the uncured resin of the mica layer, the reinforcement layer, and filler layer remained unremoved.
And, this was caused by insufficient flow or unbalanced flow of the impregnated resin in the insulating film during the curing process by pressurizing and heating to form the insulating film for windings of electrical machines, because the resin content in each of the mica layer and the filler layer in prepreg state was not at an appropriate content.
The present invention is aimed at providing insulating material for obtaining windings for electrical machines having an insulating film superior in electric characteristics, and windings for electrical machines having the insulating film superior in electric characteristics.